1. Field of the Invention
The present invention relates to an automatic tool changing device for a machine tool.
2. Description of the Related Art
In case that a tool is changed, machining accuracy on a workpiece is maintained by properly fitting a tool holder onto the spindle of a machine tool. Occasionally, however, the tool holder may not be fitted to the spindle properly because of foreign matter, such as swarf, adhered to contact surfaces of the spindle and the tool holder, which affects the machining accuracy. For this reason, there has been employed a method of cleaning a surface of a taper hole of the spindle and/or a tapered portion of the tool holder as the contact surface is cleaned by removing the swarf and the like using fluid, such as air in an operation of a tool change.
There is a known method in which an air nozzle is opened in the taper hole of the spindle to which the tapered portion of the tool holder is fitted. When the tool holder is detached from the taper hole of the spindle or when a new tool is fitted to the spindle, the pressurized air is supplied from an air supply onto the contact surfaces of the tool holder and the spindle taper hole through an air hole and the air nozzle that are provided to the spindle. Thus, swarf and the like adhered to the tapered portions of the contact surfaces of the tool holder and the spindle is removed and cleaned up by the air (see JP 52-49579B, JP 47-46705B and JP 2503170B).
The cleaning methods as described in the above publications, however, require an air passage to be provided to the spindle to blow air out from the spindle taper hole provided thereto through the air passage. The necessity for forming the air passage in the spindle complicates fabrication of the spindle.
There is another known method in which the operation similar to the tool change is performed, and a cleaning tool, such as a brush, held by a tool changing arm is pressed towards the spindle taper hole to clean the spindle taper hole (see JP 9-29577A). In this method using the extra cleaning tool, such extra leaning tool needs to be prepared. At the same time, it is also required to carry out the cleaning operation by pressing the cleaning tool towards the spindle taper hole at the time of tool change, and thereafter to exchange a new tool with the cleaning tool on the tool changing arm. This entails an additional cleaning operation for each the tool change operation, so that it accordingly takes a long time to complete the tool change, thereby lowering operation efficiency.
There is known a tool changing device in which an air passage is formed in a tool holder with an air discharge opening on a contact surface of the tool holder to be in contact with a spindle taper hole, and a tool changing arm is provided with tool gripping sections in a twin form from JP 3203598B. At the time of tool change, a tool holder attached to the spindle and a tool holder attached to a magazine pot are gripped by the two tool-gripping sections of the exchange arm. When the tool holder is held by the tool gripping section, an air passage formed at the tool changing arm and the air passage of the tool holder communicates with each other to flow air. After starting of pulling out the tool holder, the air blows out from a gap between the spindle taper hole and the tapered portion of the tool holder and sweeps away dust to clean. The magazine pot is cleaned up in the same manner. When a new tool holder is to be attached to the spindle, the cleaning is carried out in a similar way. The cleaning method described in this document requires an air passage formed in the tool holder, which makes the tool holder costly. Furthermore, since the existing tool holders have no air passage, the aforementioned method cannot be applied to the tool change using existing tool holders.
In addition, there is known an automatic tool changing device in which tool allocating means allocates a tool holder to be attached to the spindle among a plurality of tool holders held by a turret by rotating the turret by transmitting rotation of the spindle to the turret through a speed reducer, and the tool holder is fitted to a tapered hole of the spindle using up-and-down motion of a spindle head, as disclosed in JP 2535479B.